The N7620B Pulse Building corrections appear to be additive; that is, they can provide X dB improvement. To ensure that the uncorrected system performance is optimized, so that the corrected results are the best possible, there are several things that can improve the raw performance of your system:
Running the built-in PSG/MXG/EXG/ESG I/Q calibration
Minimizing the Images
Minimizing carrier leakage
Align the I/Q modulated signal to the PSG/MXG/EXG/ESG pulse modulator